1. Field of the Invention
The present invention broadly relates to gas turbine engines and, more particularly, is concerned with the inclusion of a heat pump and associated heat exchanger in a gas turbine engine for improving the overall efficiency thereof.
2. Description of the Prior Art
In many applications, gas turbine engines are operated more frequently to produce only a portion of their related maximum work output for which they were designed. Examples of such applications include the use of gas turbine engines as the primary source of power in the propulsion systems of aircraft, ships, and land vehicles. In such applications, it is common to encounter situations where over a period of time a greater proportion of the total fuel consumed in the engine occurs when the engine is operating to produce only a portion of its rated maximum work output than when the engine is operating to produced rated maximum work output. The large proportion of fuel consumption by the engine at work output levels less than the rated maximum output level results not only from the greater lengths of time of engine operation at sub-maximum output levels, but also because of inherently less efficient operation of the conventional gas turbine engine at reduced work output levels.
The overall efficiency with which a gas turbine engine operates can be expressed partially as the thermal efficiency, which is the ratio of the rate at which energy is made available to do work to the rate at which energy is released by the combustion of fuel. For conventional gas turbine engines with representative levels of component inefficiencies, greater values of the total temperature of the gas entering the high pressure turbine section of the engine, generally yield greater values of thermal efficiency. For a gas turbine engine of conventional design, the rate at which air enters the compressor section of the engine and the total temperature of the gas entering the turbine section of the engine are interrelated in a manner which necessitates a decrease in the total temperature of the gas entering the turbine section when it is desired to decrease the airflow through the engine. Therefore, since one of the principal means used to decrease the work output of a gas turbine engine below its rated maximum is to decrease the rate of airflow through the engine, it is readily seen that operation of the engine at work output levels substantially less than its rated maximum reduces the total temperature of the gas entering the turbine section and results in a substantial decrease in the thermal efficiency of engine operation.
U.S. Pat. No. 3,796,045 to Foster-Pegg proposes certain modifications for a gas turbine power plant for improving the power output and/or the thermal efficiency thereof. In FIG. 2 of the patent, an embodiment is illustrated wherein compressed air from a compressor is heated in a regenerator heat exchanger by waste heat in the turbine exhaust gases before the compressed air enters the combustor. Also, heat in the turbine exhaust gases is recovered and converted into mechanical energy for driving cooling means for superchilling inlet air to the compressor.
While the arrangements of the aforementioned patent may accomplish its intended purpose, it appears to require a rather complicated and elaborate system for doing so. Therefore, a need exists for a simpler alternative arrangement for fostering improvement in operating efficiency of a gas turbine engine.